1. Field of the Invention
The invention relates generally to ink compositions for use in capillary-action markers. More particularly, the invention relates to an ink composition, particularly a low viscosity ink composition, comprised of a solvent, a colorant particle, and a resin component.
2. Brief Description of Related Technology
Opaque markers (such as correction markers) are used to make opaque marks on paper, cardboard, glass, and other substrates. Correction markers, for example, are typically used to correct handwritten, typewritten, photocopied, and/or printed markings on one of the above substrates by forming an opaque mark capable of (1) effectively covering and concealing any undesirable markings previously made on the substrate, and (2) being written upon such that it can ‘receive’ new corrected markings.
Ink compositions for use in opaque markers (such as correction markers) typically include an opacifying pigment (e.g., titanium dioxide) dispersed in the ink composition. The opacifying pigment is typically present in sufficient quantity such that a written mark made with the ink composition on a substrate appears substantially or completely opaque. When the opaque marker is a correction marker, the opacifying pigment is present in sufficient quantity such that a corrective mark made with the ink composition on a substrate effectively conceals any undesirable markings previously made on the substrate.
Opacifying pigments (e.g., titanium dioxide) contained in ink compositions can settle over time because of the high density of the opacifying pigments relative to that of the carrier/solvent in the composition. Settling of the pigment particles occurs regardless of the particle size or shape because of the density differential between the pigment and the carrier/solvent, and ultimately results in little pigment being delivered to a substrate when a written mark is made with the ink composition. Consequently, correction markers generally include high viscosity ink compositions. As a result, corrective markers generally deliver their ink compositions using mechanisms such as a pin valve because delivery mechanisms associated with low viscosity ink compositions will inevitably become clogged.
Further, when porous substrates such as paper are used, small pigment particles tend to settle into the interstitial pores of the porous substrate after written markings are made on the substrate, thereby reducing the level of intensity and/or opacity of the written markings. Again, the foregoing effects can be mitigated by increasing the viscosity of the ink composition. For example, when conventional correction fluids having high viscosity and containing a fast drying solvent are applied to a porous substrate such as paper, some of the solvent is evaporated and some is absorbed by the porous substrate, thereby increasing the fluid viscosity at the substrate surface such that settling into the interstitial pores of the porous substrate is largely avoided. This approach, however, is not suitable for conventional capillary-action markers because such marker systems require very low viscosity inks (typically less than 40 centipoises).
Conventional capillary-action markers contain a fibrous reservoir and a nib in fluid communication therewith, and therefore do not allow ink compositions contained therein to be effectively mixed (once the marker is loaded with ink). Further, the marker's reservoir fibers and/or nib can undesirably filter any opacifying pigments contained therein and become clogged over time. Accordingly, over time, the marker is generally rendered incapable of making substantially opaque markings. Thus, it has been particularly difficult to achieve long-lasting opaque capillary-action markers containing conventional opacifying pigments because such marker systems require low viscosity inks, do not accommodate mixing, and often become clogged.